we're learning more about what sparked the fbi investigation that ultimately led general david petraeus to resign his post as cia director. officials say he was never under investigation. marla tellez joins us in our studio with what they have learned overnight. >> reporter: the fbi's investigation began with a woman who worked for the state department and overnight she has been identified as jill kelly. kelly, who was a personal close friend of general david petraeus, said she was receiving anonymous, harassing e-mails from someone. well, that someone turned out to be paula broadwell, petraeus' mistress. the nature of those e-mails has not been disclosed. it was during this investigation that fbi agents discovered e-mails between broadwell and petraeus they say were indicative of an extramarital affair, which led to general petraeus' resignation on friday. senator dianne feinstein, who heads up the senate select committee on intelligence says the news hit her like a lightning bolt. >> broadwell sent these threatening e-mails to her and she was frightened and she went to the fbi. oh, i